Various independent electronic ignition timing control systems and electronic air-to-fuel ratio control systems are known and used in the art.
Ignition timing, also referred to as spark timing, is an important aspect in the performance of internal combustion engines and has been widely utilized over the years. Generally, ignition timing relates to how early or late the spark plug fires in relation to the axial position of the piston within the cylinder. For instance, when the engine is being operated at high speeds it is desirable to initiate the combustion process early, such that the combustion reaction has adequate time to develop and assert its force upon the piston. Thus, the ignition timing control system delivers a spark to the combustion chamber before the piston reaches a top-dead-center (TDC) position, an occurrence commonly referred to as timing advance. Conversely, if the engine is being operated at relatively low speeds, the control system instructs the spark plug to fire at a point closer to TDC (either slightly before or slightly after). In the case where the spark plug fires slightly after TDC, a timing retard has occurred and allows less time for the combustion process to develop. Manipulation of the ignition timing is helpful for optimum performance, and has been widely utilized according to a multitude of techniques.
Vehicle ignition timing control systems often use microprocessor-based closed loop circuits to receive electronic inputs from throughout the vehicle and adjust the ignition timing accordingly. These inputs can vary widely, but typically include operating parameters such as engine speed, intake manifold pressure, intake air temperature, throttle position, engine exhaust emissions, etc. By adjusting the ignition timing according to readings sensed around the engine, the timing control system is able to adapt to changing conditions and thereby enables the engine to operate more efficiently and with decreased exhaust emissions. While the closed loop feedback utilized in these types of timing systems contributes to the overall performance of the engine, other factors need to also be considered.
For example, the ignition timing needs of the engine when it is initially started up vary considerably from those of the engine once it has been running and is warm. Similarly, ignition timing needs of an engine during an idle period are different from those required by an engine experiencing significant acceleration. Thus, a single closed loop feedback routine for ignition timing may not be ideal across a wide spectrum of operational modes.
The air-to-fuel ratio of the combustible mixture being provided to the combustion chamber also affects the operating characteristics of the engine. The air-to-fuel ratio of the mixture refers to the relative amount of air to fuel in the combined mixture being supplied by the carburetor to the engine. By increasing the percentage of fuel in the combustible mixture, the mixture becomes “richer”, while increasing the percentage of air has the effect of making the mixture “leaner”. During high load conditions, such as when the engine is initially being started or when the engine experiences a sudden acceleration, a richer mixture is often desired. Likewise, during low load conditions, such as when the engine is experiencing a rapid deceleration, a leaner mixture may be advantageous.
For example, the electronically controlled carburetor disclosed in U.S. Pat. No. 6,273,065 B1 and issued to Tecumseh Products is capable of controlling an air/fuel mixture supplied to the engine. According to this patent, a rotating flywheel carrying a magnet induces a pulse which is fed to an electronic control unit. The electronic control unit utilizes this information to control the discharge of stored energy to either a spark plug or to a solenoid, which is part of the carburetor and controls or adjusts the amount of air introduced into the air/fuel mixture. In this manner, the electronic control unit is capable of enriching or enleaning the air/fuel mixture.
Large automotive vehicle engines often have complex electronic control systems with numerous sensors measuring engine parameters such as intake air temperature, engine temperature, mass air flow, exhaust emissions, and engine speed. Smaller low cost, light duty combustion engines, however, do not have the same luxury. In an effort to minimize cost and stay within significant electric power consumption and spatial constraints, small engines utilized in low cost light duty applications may only be able to adjust the ignition timing and/or the air-to-fuel ratio according to one or two input parameters.
Accordingly, it would be advantageous to provide a small, low cost control system that included both an electronic ignition timing control and an air-to-fuel ratio control for use with a small displacement engine. Furthermore, it would be desirable if that control system was capable of utilizing a limited number of parameters, as well as independent operating sequences, to improve the performance and emissions of the engine.